Whats the best design of trailer for this model mine has 2 smooth plastic rails that run underneath the edge of aluminium floor also center rollers .Ive seen the ones that support the tubes but does grit become a problem with that design?

Well, It seems that most sib trailers are set up to support the tubes. But I don't subscribe to that method for my zodiac futura mk2. I have the rails supporting the aluminum floor. I also have two small supports forward to keep the bow from bouncing up and down on rough dirt roads. I tow my inflatable with a four wheel drive pick up down dirt roads in Mexico. Abrasion hasn't been a big problem, but I do get some on the floor material where the supports are and I would rather not have that on the tubes. The floor is much easier to repair.

The biggest reason I support the boat this way is because the tubes need to be kept fairly well inflated to support the rest of the boat if the rails are under the tubes. I travel a lot and the boat goes through some big temperature changes. I would either have to keep checking and changing the pressure or I would have issues with over inflation or too little support for the load. Since the boat has the aluminum floor I can relax a bit as we go from intense sun to cool evenings with fog without worrying about it. I do have a transom saver supporting my outboard too.

As long as the rollers are wide and flat that shouldn't be a problem, but if they are narrow and have more angle on them they may only contact the floor material and underlying aluminum floor sections in a narrow spot. That is not good.

Remember, most people aren't traveling far, they may or may not have an aluminum floor and they aren't rolling down dirt roads for hours on end. The abrasion and inflation issues may not apply to you either, but plan for the conditions you will experience.

The floor fabric should have some degree of bunk support. If the boat accumulates a significant amount of rainwater while uncovered on a trailer, the weight of the water puts a lot of strain on the floor fabric. It will tend to look like the beak of a pelican that is full of water. If the boat is being jostled while being towed on a trailer, the weight of all that water bouncing up and down can cause a lot of damage to the boat.

My trailer bunks are just next to the speed tubes on the inside. The transom is supported by the bunks. In fact they extend past the transom by about 8 inches. There is also a couple of rollers in the middle. At some point I should really add in some side bunks to make putting it on the trailer easier in rough areas. For the Pacific trailer I also built a tongue extension to keep my vehicle as far away from the surge as possible. The extension is stored in a mount under the boat. Gives me a spare ball too.

Even with the keel tube inflated the flexible floor fabric deforms/bends where the bunk rails are and contacts the floor, but I deflate the keel tube on any long haul so the material isn't being stretched tight and the boat sits firmly against the bunk rails when strapped down.

Supporting the transom one way or another is definitely important.

The two small support pads up front really keep the boat from bouncing up and down on rough dirt roads.

When I reconditioned my trailer I replaced all of the hardware like the u bolts holding the axle assembly with stainless steel. I also reinforced the the joint where the trailer sections join with a cross piece. The first photo (of a floor repair) also shows the two vertical bow supports. The second image is of the added frame reinforcement. Lots of trailers and boats on the side of the road in Mexico! I'm glad I took the time to get the trailer right before I started bounding over dirt roads.

Anyone towing in dirty gritty conditions should have a full cover and chafing protection on all tie down lines.

The little black patches visible in the first picture cover wear spots from the previous owners repair attempts, those patches are not there to hold the floor to the tubes.

Even with the keel tube inflated the flexible floor fabric deforms/bends where the bunk rails are and contacts the floor, but I deflate the keel tube on any long haul so the material isn't being stretched tight and the boat sits firmly against the bunk rails when strapped down.

Supporting the transom one way or another is definitely important.

The two small support pads up front really keep the boat from bouncing up and down on rough dirt roads.

When I reconditioned my trailer I replaced all of the hardware like the u bolts holding the axle assembly with stainless steel. I also reinforced the the joint where the trailer sections join with a cross piece. The first photo (of a floor repair) also shows the two vertical bow supports. The second image is of the added frame reinforcement. Lots of trailers and boats on the side of the road in Mexico! I'm glad I took the time to get the trailer right before I started bounding over dirt roads.

Anyone towing in dirty gritty conditions should have a full cover and chafing protection on all tie down lines.

The little black patches visible in the first picture cover wear spots from the previous owners repair attempts, those patches are not there to hold the floor to the tubes.